1. Field of the Invention
The present invention relates in general to automatic transmission hydraulic control and more particularly to an arrangement for discharging band servo operating hydraulic pressure in an automatic transmission.
2. Description of the Prior Art
An example of this kind of arrangement is shown in FIG. 5, which is utilized in an automatic transmission of the General Motor's THM700 type. In the figure, a transmission case is shown having a joining surface 1a to be joined with a control valve body (not shown), a brake chamber, a servo release passage 3 extending from the joining surface 1a toward the brake chamber 2, a discharge valve 4 for discharging band servo operating hydraulic pressure, a brake band 5 which is controlled by a band servo 8, a piston 6 of the band servo 8 and a cylinder chamber 7 of the band servo 8.
In the prior art arrangement, the discharge valve 4 needs to be inserted into the servo release passage 3 through its open end at the joining surface 1a and be pushed deeply thereinto, i.e., deeply toward the brake chamber 2 side. Such an insertion results in an awkward and difficult assembling work, a complex structure of the discharge valve 4 and therefore expensive manufacturing and assembling costs.